The diagram on the Vanner website shows using their equalizer to have the 24v alternator charge the house batteries, two in series as normal, and tap off the bottom battery for house 12v. The equalizer keeps them equal. No problem. What I don't quite understand is what you use the top battery for? Is it just there for the equalizer to work and to let the alternator charge the house batteries? Or do you typically run some loads off it, just not chassis ground loads?

Second question is can you use two 12 volt chargers to charge the house batteries, at the same time, without disconnecting everything? Just discoonnect the Vanner? Or do you have to completely isolate each battery?

Usually it is "better" to run a second Vanner with a 24v house system. Use a isolation solenoid. Sean gave us a few links from the Grainger website that will allow us to charge the bus system and house system.

If you have a 24 volt coach, I recommend a 24 volt house system. Use the center tap and the Vanner to drive 12 volt loads from the 24 volt house system, but try to get the big items in 24 volts. Specifically, if you plan to have an inverter, get a 24 volt model. Lights and bulbs are readily available in 24-volt, there are a few pumps available this way, and even such items as Webasto heaters and DC refrigerators are all available in 24 volts. You will only need the center tap for a handful of controls (RV-type fridges and water heaters) and fans (RV-type furnaces, FanTastic vents).

Some folks are dead set against 24 volt house systems for whatever reason, and for those people I recommend you change the big alternator to 12 volts, and put a small belt drive unit in for the 24 volt chassis loads. Trying to run a 300+ amp 12-volt system from a 24-volt alternator is bound to lead to problems.

Your questions are so rudimentary that I think the Pro's are missing them. Not being critical now, honest.

What I don't quite understand is what you use the top battery for?

You have a 24 volt "bus" system. The bus engine starter uses 24 volts. There are 2 12 volt bats connected in series to get that 24 volts for starting. Also, bus lights and the air dryer, etc. all use the 24 volts. That is what the "top battery is "for"......to make 24V. Both are 12 volt bats.

Or do you typically run some loads off it, just not chassis ground loads?

The bus system was installed before the conversion and functions independently.....or could. Often the house system is 12 volt. You can get away without installing a separate battery bank for 12 volts by using a Vanner. The Vanner lets you tap off 12 volts from the 24 volt bus system. Normally, that would draw down a single battery in the 24 volt system. The Vanner magically taps off 12 volts and somehow uses both batteries to do that and both batteries get discharged a "little" and the 12 volts can be drawn for twice as long.

Sean is telling you that if you use 24 volts for the house DC system you will do better all around....and he is right. 24 volts uses smaller wire and handles 1/2 the current. Also, you can use the BUS charging system to charge your house bats as everything is the same voltage. The reason to "not" do this is that 24 volt STUFF is more expensive than 12 volt stuff that does the same thing. And, 12 volt stuff is readily available EVERYWHERE. The vote has been cast by the RV and bus converter industry. They build 12 volt house systems, as far as I know. Using a Vanner for 12 volts is a problem in that the Vanner usually can't handle the full load of the house cause a beefy Vanner like that is expensive and not efficient. Sean designed his system from the ground up and I think he has a Vanner to make 12 volts for only those systems he can't get in 24 volts. Now, that gives me paws cause he is the kind of knowledgeable guy that could "build" stuff that would run on 24 that used to use 12.

and tap off the bottom battery for house 12v.

I know it looks like that is what is happening. Actually, the Vanner is providing power from "both" batteries.

OR! "who ya gonna believe? Me or your lie'n eyes".

I am actually repeating everything everybody else has said to you. I just used more words. They did have it covered. If this didn't help you out Fellow Knut, well, just ignore it and my meddling.

John

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Thanks. I think I was making it too complicated for myself. I was an electronics tech years ago when I earned an honest living, but I was a lot more comfortable inside the guts of modems and computers than inside of power systems!

My bus got delivered a couple of hours ago, during the walk through there was a Vanner system installed but the PO didn't know what it was and had never used it. He just had a 12 volt battery and a cheap charger running completely separately from the coach batteries.

What I want, ideally (i think, probably wrong) is the chassis batteries set up so they can be separate from the house batteries, or connected so the house batteries can be charged going down the road. The house batteries will have a 24 volt load running an inverter, and 12 volt loads for things like furnace, water pump, fridge. There will be no 12 volt load from the chassis batteries. So I think I can connect the house batteries to the 24 volt chassis system through a switch, have the Vanner connected to the house batteries, pull the 12 volt power from the mid-point of the house batteries, and the Vanner will keep everything equal. The Vanner will have no effect on the chassis batteries.

Brian, how are you equalizing your 24 volt "bus chassis" batteries? That was the reason for the Vanner.

You can purchase another Vanner for your 24 house battery system and pull your 12volts for your fridge and heater and misc other devices.

The inverter thread down a couple lines discusses which battery bank isolator that is/are recommended. This will allow you to drive down the road and charge or maintain "both" battery banks. There are used Vanner equalizers on Ebay or Bus/Transit salvage yards. The little investment now will save your batteries.

... The reason to "not" do this is that 24 volt STUFF is more expensive than 12 volt stuff that does the same thing.

John, I actually disagree with this and believe that it is a widely held myth.

It's easy to see where this comes from, because, for example, a 10-watt halogen bulb in 12 volts costs less than half what the same bulb costs in 24 volts. However, the big ticket items are really the other way around.

For example, if you want a 2,000-watt inverter, there is no price difference whether you buy that in 12- or 24-volts. However, the 12-volt model will cost a lot more to hook up -- figure to spend twice as much for the DC cables and crimps, and 50% more for the fuses and disconnect switches.

OTOH, if you want a 4,000 watt inverter, you will save a ton by going with 24 volts -- there are no 4,000-watt inverters in 12-volt, and so you need to buy two 2,000 watt models, for 50%-70% more, plus all the duplication of cables, crimps, and extra terminals.

Fuses and circuit breakers for your DC loads are either the same price or less money for 24-volt than 12. That's because below 30 volts, it's all the same stuff (there is no difference between a "12-volt" breaker and a "24-volt" breaker), but you will use lower values for 24-volt loads than 12-volt, and when there is a price difference in these items, it is always the higher current items that are more expensive than lower current items.

Sensor VSD pumps and Danfoss compressors are dual voltage -- they run on 12 or 24. Webasto heaters are the same price in either voltage.

You will also save a ton of money (and weight) on battery cables, inter-ties, solenoids, and DC load wiring by using 24 volts instead of 12. And, of course, if you have a 24-volt alternator, charging a 12-volt house system from the main engine will cost a bundle.

All of this far outstrips the extra cost of 24-volt bulbs (the fixtures are the same -- no such thing as a "12-volt" incandescent fixture vs. a 24-volt one) and even the cost of a 30-amp equalizer.

Lastly, I will point out that 120-volt items are almost universally less expensive than low-voltage DC items to do the same thing, and that includes lights, pumps, and even refrigerators. So it can be argued that, to save money on individual components, you should use more 120-VAC stuff, and get a bigger inverter, which, as I said, is cheaper to do in 24 volts. (The downside to this, of course, is that you pay a loss penalty through the inverter, so this is not the best strategy for extended boondocking)

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And, 12 volt stuff is readily available EVERYWHERE.

Well, OK, it's easier to find 12-volt bulbs and pumps. But how hard is it to carry a spare bulb or two?

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The vote has been cast by the RV and bus converter industry. They build 12 volt house systems, as far as I know.

Every major bus converter uses 24-volt house systems when starting with a 24-volt bus chassis. They use 24-volt inverters and 24-volt distribution panels, and convert down to 12-volts with a battery equalizer for those things that simply don't come in 24-volt, like FanTastics.

The rest of the "RV industry" works on 12 volts because that's the alternator voltage provided to them by the chassis manufacturers. If you start out with a Ford F450 it makes just as little sense to put in a 24-volt house system as it does to put a 12-volt system into an MCI or Prevost. Less, actually, because stepping the 12-volts up to 24 to get any alternator-driven battery charging is much harder than tapping a 24-volt system to get 12 volts where needed.

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Using a Vanner for 12 volts is a problem in that the Vanner usually can't handle the full load of the house cause a beefy Vanner like that is expensive and not efficient.

That's not how an equalizer works. The equalizer does not need to be able to handle the full load -- the batteries do that. The equalizer then makes it up over time. This is why you draw the load off the center tap and the equalizer is also connected there. It's possible to use a Vanner as a straight voltage converter (no center tap connection -- only the loads are connected to the output), in which case you do need one sized for the full load -- but then it's not really an "equalizer." You size an equalizer based on the time average of the 12-volt loads, usually only a small fraction of the total, and not the maximum possible 12-volt load.

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Sean designed his system from the ground up and I think he has a Vanner to make 12 volts for only those systems he can't get in 24 volts. Now, that gives me paws cause he is the kind of knowledgeable guy that could "build" stuff that would run on 24 that used to use 12.

Not much knowledge required, for what I did. I changed all the incandescent bulbs to 24-volt items I bought on the Internet. For the handful of places I wanted to use LEDs, I simply wired them together in series pairs. I sold my 12-volt Webasto on eBay and bought a 24-volt one for the same price. And, of course, I bought a 24-volt inverter, two 24-volt water pumps, and a 24-volt fridge.

Weeelllll is my face red, or what? On the contrary, thank you for all of that. I think there might be some that were of the same mind as I. Certainly, I think, you have sorted it all out.

I don't have a problem with eating crow or humble pie, either one. The nice thing about being wrong is that I am certain that I am learning something. But! There is always a BUT. As far as my complimenting you on you tech prowess.....yeeeesssh. Wrong again! You can be justifiably proud of your humility.

Thank you Sean,

John

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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.The price of apathy towards public affairs is to be ruled by evil men." Plato “We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”—Pla

Don't forget that the busses come with flo lites that by using the ballast you can convert 120 volt unit to 24 volts.Problem with the bulb change is that all the bus bulbs are two pin and all rv lits are single pin. Jerry

All your posts come across as being constructive and informative. Always have. No worries about that.

Now about your making funny faces and sounds when I talk.....that has to STOP.

Be well and happy,

John

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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.The price of apathy towards public affairs is to be ruled by evil men." Plato “We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”—Pla